The present invention relates to mechanisms for driving punch pins in a punching apparatus. More specifically, it relates to a device for driving punch pins in a punching apparatus that punches a ceramic green sheet during the formation of a ceramic substrate, as well as to a clutch mechanism for coupling a punch pin with its drive shaft.
An example of a conventional punching apparatus for forming holes in a ceramic green sheet (hereinafter simply referred to as "a green sheet") is disclosed in Japanese Patent Unexamined Publication No. 55-91617.
In the disclosed apparatus, a plurality of punch pins are supported by an upper plate of a die set, and are disposed at predetermined intervals. A plurality of pairs of solenoids are disposed, each pair corresponding to one of the punch pins. One of the solenoids in each pair is energized so as to move the punch pins to their respective working positions or stand-by positions. Thereafter, the upper plate of the die set, supporting the punch pins, is vertically moved so that the punch pins at their working positions cut holes in a green sheet.
Since the solenoids are always in their state of being energized during operation, they generate a great amount of heat. In order to dissipate heat, cooling is generally effected by adopting a liquid cooling system.
Such a conventional punching apparatus has the following drawbacks. As described before, the punch pins are moved to the working or stand-by positions by electromagnetic force generated by the solenoids. If the electromagnetic force generated by the solenoids is not sufficiently strong, the punch pins may undergo unwanted axial movement during working, resulting in no punching action being performed. On the other hand, if the magnetic force generated by the solenoids is excessively strong, this may result in the solenoids generating heat in such a great amount that the dissipation of heat cannot be performed easily.
The punch pins are connected to the solenoids for driving the punch pins by magnets. If the attractive force of the magnets is not sufficiently strong, in the event that any of the punch pins becomes caught by, e.g., a portion of a separation plate capable of being inserted, the punch pin may become separated from the magnet to remain at a descent position. With the above-described arrangement, therefore, the behavior of the punch pins can be irregular.
On the other hand, if the attractive force of the magnets is excessively strong, in the event that the axis of a punch pin is deviated from that of the magnet by, for instance, the difference in thermal expansion between the proximal portion and the separation plate, the punch pin may become bent, thereby involving the risk of its breakage.